A comprehensive new documentary on Elvis Presley is heading to HBO next month, and a sneak peek from the upcoming film sheds some light on the King of Rock ‘n’ Roll.

Titled Elvis Presley: The Searcher, the documentary chronicles his creative journey from childhood through to his final recording session, which took place in the famed “Jungle Room” at Graceland.

The rock icon’s ex-wife Priscilla Presley, who’s also an executive producer on the film, debuted Elvis Presley: The Searcher at SXSW, and spoke about his “final chapter” as she candidly discussed his deep addiction to prescription drugs that ultimately led to his death at age 42.

“It was difficult for all of us, we certainly didn’t see it coming,” said Presley, People reports. “But we certainly saw the journey he was taking.”

She added: “People go, well, ‘Why didn’t anyone do anything?’ Well, that’s not true. People there in the inner group did, but you did not tell Elvis Presley what to do. You did not. I mean, you’d be out of there faster than a scratched cat. They would try and no way. He knew what he was doing.”

She also shared her belief that it was his time in the army that began his relationship with pills. “That was the thing — they gave them to the soldiers over there to keep them awake,” she said. “He was on guard at that time. He had maneuvers that he had to do late at night, so the pills were given to the guys and that’s how he started. And if you take a sleeping pill, you have to do something to get yourself awake. … He was in unchartered territory, he truly was, and he did this and tried to do this alone.”